Behavioural Neuroscience - The Neuron Flashcards
Overview of what is covered in this study deck:
Neurological Bases of Behaviour
The Neuron
-Neuronal Communicaton
-Structure of the Nervous System
-Brain Damage and Disorders
Structure of the neuron
Neural communication
Classes of Neurotransmitters
The Neuron Structure
-Cell body (soma)
(where the nucleus is and stores information)
-Dendrites -listeners
(receive info. from other cells and message travels to base of soma)
-Axon- speakers
-Axon Terminals
(neurotransmitters in vesicles that pass message to other cells)
The Neuron (3 types)
-Motor neuron
-Sensory neuron
-Interneuron
Motor Neuron
-Send messages out to
body’s tissues FROM the
brain
-in spinal cord
Sensory Neuron
-Carry messages from
sensory organs and
tissues TO brain and
spinal cord
-pick up information from the periphery of the body
Interneuron
Neurons communicate
with EACH OTHER within
brain and spinal cord
Neural Communication
ELECTROCHEMICAL
ELECTROCHEMICAL
ELECTRO- shift in electrical charge
that travels along the axon
CHEMICAL- Release of neurotransmitters
that travel from one neuron to the next
Neural Communication
2 types of potentials
-Resting potential
-Action potential
-Resting potential
Inside of neuron is more negatively charged than outside (polarized)
-70mV
-When a neuron ”fires”, channels open and close causing this balance to be shifted (depolarized)
Action potential
A shift in electrical charge, starting
at the base of the axon, and travelling down its length
Neural Communication:
-Channels open up, causing positive ions to rush in, causing the next set of channels to open up.
-Na+ channels previous ones close as action potential moves along axon
Neural Communication
1)At rest, the inside of the cell is more
negative than the outside… when
possible, positive ions want to rush
in
2) Stimulation from dendrites affects
the electrical charge; when it
reaches the voltage threshold or
threshold of excitation (-55 mV) →
action potential
3) When an Action Potential begins,
sodium channel opens and
positively charged sodium (Na+) ions rush into the cell, making charge positive (depolarization)
4)Sodium channels close, and
potassium channels open.
Potassium (K +) exits, bringing
charge back to resting potential.
5) Eventually, the K+ channels close
as well, but by that time, too
many positively charged ions
have left the cell. Cell must now
reset to prepare for next action
potential.
Action potentials are ‘all-or-none’
When reaches threshold, all the same no matter strength of stimulus (how far it goes beyond threshold)
The Importance of Myelin
-Each neuron’s axon is wrapped by
a fatty myelin sheath
− Supplied by surrounding glial cells
-Myelinated axons only allow action
potentials to occur at the
unmyelinated Nodes of Ranvier
-The signal “jumps” from one node
to the next, allowing for faster
transmission
- Saltatory Conduction: the rapid method by which nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier
Multiple Sclerosis (MS)
-Immune system turns on the body
−Causes hardening of the myelin insulation
-Environmental and genetic factors are contributors
−Positive correlation between risk and distance from equator
−Identical twins have 33% chance of developing MS
-Symptoms typically develop between 20 and 40 years
−Women are 3 times as likely as men to develop MS
MS: Symptoms and Treatment
Visual, Sensory, Motor symptoms:
−Optic Neuritis - painful vision loss
−Reduced balance and fine motor control
−Constant state of tiredness
−Numbness or tingling in the extremities
- No cure is available for the disease
−Focus is on treatment of symptoms and
modifying the course of the disease
(e.g., interferons)
How do Neurons Send Messages?
-Synapses: gaps between neurons
-Neurotransmitters: chemical messengers released after an action potential that travel across this gap
− Neurotransmitters are uniquely shaped
− Can only bind to certain receiving dendrites
− Neurotransmitters can have excitatory or
inhibitory effects on the receiving neuron (Na+ or K+ channels)
− Any remaining neurotransmitter in the synapse is diffused into ECF, degraded, or reabsorbed (reuptake) into descending neurons
gaps between neurons
synapses
Chemical messengers released after an action potential that travel across this gap
Neurotransmitters
Synaptic Transmission
-action potential reaches axon terminal
-calcium channels open
-Ca2+ causes vesicles to release neurotransmitter
-Neurotransmitter crosses synapse
-neurotransmitter binds to neuroreceptors
-trigger signal in post-synaptic neuron
Neurotransmitters and Functions
Glutamate
-Excitatory; linked to forming memories
-Excessive amounts of this neurotransmitter implicated in triggering of seizures
Neurotransmitters and Functions
GABA
Inhibitory; influences muscle tone (reduces tension), facilitates sleep, reduces arousal; Epilepsy meds increase action of this neurotransmitter
Neurotransmitters and Functions
Acetylcholine
(ACh)
Found at the neuromuscular junction (contact between motor neuron and muscle fiber); controls movement; Role in attention and memory (cognitive functioning)
Neurotransmitters and Functions
Serotonin
(5-HT)
Serotonin
(5-HT)
Affects mood (emotions), hunger, sleep etc.
Serotonin levels may be linked to depression (not enough serotonin in brain)
- Prozac (drug) raises serotonin (blocks reuptake into descending neuron)
Neurotransmitters and Functions
Dopamine
(DA)
Dopamine
(DA)
Involved in reward & pleasure, learning (about things we find rewarding, like money), movement
Abnormal levels in schizophrenia (high dopamine), ADHD and Parkinson’s (low dopamine)
Basic Mechanisms of Drugs
What is a drug?
Exogenous (outside body) substance, not necessary for normal function, which alters the functions of cells
Basic Mechanisms of Drugs
Drugs cause changes in - and -
-Ritalin
-physiology and behaviour
-blocks reuptake of dopamine (increased attention)
Basic Mechanisms of Drugs
Ritalin blocks
reuptake of dopamine - increased attention
Basic Mechanisms of Drugs
What is a psychoactive drug?
Ritalin is -, Tylenol is -
A chemical substance that alters perceptions and mood
-Ritalin is psychoactive, Tylenol is not
Drugs and Neurons
Drugs affect brain – at synapses
AGONIST
-brain chemistry
-Increase or mimic effects of neurotransmitter – AGONIST (drug that can block reuptake or increase production of neurotransmitters)
Drugs and Neurons
Black Widow Spider venom
-Increases release if Ach
-violent muscle contractions
Drugs and Neurons
Prozac
-blocks reuptake of serotonin leaving more in the synapse
-relieves depression symptoms
Drugs and Neurons
-Drugs affect – at -
-Antagonist
-brain chemistry at synapses
-block or inhibit effects of neurotransmitter - ANTAGONIST (prevent it from being released, decrease production of neurotransmitter and prevents it from binding)
Drugs and Neurons
Botulin
-Blocks release of ACh
-Causes paralysis
Drugs and Neurons
Curare
-Blocks ACh receptor site (cannot bind to next neurons)
-causes paralysis (plant abstract poison that is used as a paralyzing agent)
Action potential STEPS
Put it all together
- Charge at rest is negative (-70mV)
- Neurotransmitters bind with receptor sites on dendrites
* Excitatory: Sodium
channels open (Na +
enters, charge becomes
more positive)
* Inhibitory: Potassium
channels open (K + exits,
charge becomes more
negative) - If charge reaches threshold, action potential begins
- Sodium channels open at the base of the axon, Na + rushes in, charge jumps up to peak, triggers adjacent sodium channels to open, etc. down the axon
- Potassium channels open, K +
exits, bringing charge back to
resting potential - When AP reaches the axon
terminals, it opens calcium
channels, causing CA2 + ions to
rush into the terminal, and
release neurotransmitters - Neurotransmitters travel
across the synapse and bind
with post-synaptic neuron
